1. Field of the Invention
The present invention relates generally to apparatus and methods for pressurizing a closed vessel in the form of a container used to store a liquid such as a liquefied gas so that pressure within the container may be increased, maintained or otherwise controlled. More specifically, the present invention relates to utilizing thermoelectric cooler/heater configurations to vaporize a portion of a liquid such as a liquefied gas by contact with a heating surface of the thermoelectric device, while cooling the remaining portion of the liquefied gas within the container by contact with a cooling surface of the thermoelectric device.
2. State of the Art
Supplying of pressurized gases of various types may be required for manufacturing processes, powering vehicles, as well as other uses. Typically, liquefied gases may be stored within containers or vessels and the gas within may be removed for use as needed. If the gas is not used, pressure may build within the container, and gas may be released so that pressures do not exceed a maximum pressure within the container. Containers or vessels for storing liquefied gas may also be insulated so that the liquefied gas therein may be stored in a liquid state for extended intervals of time. Therefore, the ultimate volumetric supply rate of pressurized gas from a liquefied gas container may be limited by the amount of heat energy that may be transferred through the container, by which heat energy the liquefied gas is vaporized.
One prior art solution to the limited gas supply from liquefied gas storage containers comprises heating the liquid within the container to the desired saturation pressure, thereby increasing the amount of gas that may be used. However, in situations where demand for the pressurized gas varies between relatively high volumes and relatively low volumes, such as in the case of a liquefied gas powered vehicle, heating the entire volume of the liquefied gas may have deleterious effects upon the storability of the liquefied gas when the demand for a large volume of gas diminishes.
A second prior art solution removes liquid from the tank and uses ambient heat to vaporize it, thus providing for relatively high volumes of gas to be used. However, merely adding heat to the liquefied gas does little to improve any capability for long term storage of the liquefied gas that remains within the container. Furthermore, such systems may be difficult to control or configure in some applications, such as within fuel tanks on heavy duty vehicles powered by a liquefied gas, such as natural gas.
U.S. Pat. No. 4,593,529 to Birochik discloses a thermoelectric heat pump that is used to control the temperature and pressure of confined substances, particularly carbon dioxide. Birochik discloses that a heat pump may be used to heat or cool the confined substance. In essence, this is similar to prior art solutions of adding or extracting heat from the bulk of the liquefied gas, but uses a heat pump. Therefore, the heat pump of Birochik may have detrimental effects upon the storability of the liquefied gas by adding external heat to the liquefied gas within the container in the manner of other prior art approaches.
In view of the foregoing, an apparatus and method for delivery of pressurized gas from a liquefied gas container which improves on conventional apparatus and methods and eliminates many of their respective disadvantages would be desirable.